Since the first observation of carbon nanotubes(CNTs) in 1991, extensive research has been done on the synthesis methods and its applications. Among the synthesis methods, chemical vapor deposition(CVD) has many advantages such as high purity, high yield, simple process, selective growth, vertical alignment and large area uniformity. The reaction temperature of thermal CVD is generally as high as 700-1000℃. One of most attractive applications of CNTs is an electron emitter for flat panel displays such as field emission display(FED), vacuum fluorescent display(VFD).
In order to apply directly grown CNTs by CVD method to an electron emitter on the soda-lime glass substrate, the growth temperature must be lower than 550℃. Soda-lime glass, which has softening at 550℃, is commonly used as the substrate of flat panel displays because of low price and good vacuum sealing. Because of this temperature limitation, most of researcher used pre-made CNTs by arc discharge method as an electron emitter. In this work, a new fabrication method was suggested to grow CNTs at lower temperature than 550℃. It is not only simple growth technic but also applicable to mass production.
Ag thick films were coated using screen printing method on the glass substrates. One of coating method for Ni catalyst was electro-plating on the Ag film and another method was Ni powder mixing with Ag paste. CNTs were grown on the Ni catalyst by thermal CVD from 500 to 550℃. CNTs were analysed with SEM, TEM, Raman, α-step and field emission tester. Low temperature(500-550℃) grown CNTs reveal poor crytallinity, but have a good field emission characteristics. The turn-on fields were about 2.5-3.5 V/μm with an emission current density of 10 μA/㎠, and the threshold fields were about 3.8-4.5 V/μm with an emission current density of 1 mA/㎠, and β factors were about 3000-4000. Fowler-Nordheim plots showed good linear fit, indicating that the emission current of CNTs followed the Fowler-Nordheim behavior.
In order to increase the electron emission with low edge emission, total emitted current density and edge emission factor of CNTs were simulated by the variation of CNTs inter-distance and cell-gap. The total emitted current density was maximized at the condition of CNTs inter-distance is about 2-3 times of CNT length. At the high CNT density condition, electric field screening effect of neighboring CNTs deeply influenced limitation of local electric field on the CNT tip. To reduce edge emission, the lower cell-gap was necessary, but arcing and electric short problems were occurred at the very small cell-gap. After all, the optimum cell-gap was about 2-3 times of CNT length.
